\documentclass{article}\begin{document}
\declare{syntax={infix,99,"+",l}, meaning=arith1.sum,thisis=nonsemanticdata}
\begin{theorem}
\declare{syntax={infix,100,"/",l}, meaning=artih1.divide}
\declare{syntax={infix,99,"-",l}, meaning=arith1.minus}
\declare{syntax={infix,100,"*",l}, meaning=arith1.times,thisis=nonsemanticdata}
$(2*3)$
$${2+{ab}}/2$$
\end{theorem}
\begin{proof}
\declare{macro=\gcd, meaning=arith1.gcd, argspec=[2], code={...}}
\declare{macro=\gcd2, meaning=arith1.gcd2, argspec=[2], code={...}}
$1+1$
\end{proof}
\begin{lemma}
$2+2$
\end{lemma}
\end{document}

